401 Unit 3 Exam Spring 2018 (Buffers, Titrations, Ksp, & Transition Metals)

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1 Seat# : 401 Unit 3 Exam Spring 2018 (Buffers, Titrations, Ksp, & Transition Metals) Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. (3 pts each) 1. Which of the following combinations would be the best to buffer the ph to 7.0? a. H 3 PO 4 and H 2 PO 4-, K a = b. HNO 2 and NO 2-, K a = c. CH 3 CO 2 H and CH 3 COO -, K a = d. H 2 PO 4 - and HPO 4 2-, K a = e. NH 4 + and NH 3, K a = All of the following statements concerning buffers are true EXCEPT a. buffers are resistant to changes in ph upon the addition of strong acids. b. buffers are resistant to changes in ph when diluted with water. c. the ph of a buffer is close to the pk a of the weak acid from which it is made. d. buffers contain appreciable quantities of a weak acid and its conjugate base. e. buffers are used as colored indicators in acid-base titrations. 3. Which one of the following conditions is met at the equivalence point of the titration of a monoprotic weak acid with a strong base? a. The volume of base added from the buret must equal the volume of acid titrated. b. The moles of based added from the buret equals the initial moles of acid. c. The molarity of the base equals the initial molarity of the weak acid. d. The percent ionization of the base must equal the percent ionization of the acid. e. The ph of the solution is equal to or less than What is the electron configuration of Cr? a. [Ar]3d 6 b. [Ar]4s 1 3d 5 c. [Ar]4s 2 3d 4 d. [Ar]4s 2 4p 4 e. [Ar]4s 1 4p 5 5. What is the effect of adding sodium hydroxide to a solution of benzoic acid, C 6 H 5 CO 2 H? 1. The ph increases. 2. The concentration of C 6 H 5 CO 2 H decreases. 3. The concentration of H 3 O + increases. a. 1 only c. 3 only e. 2 and 3 b. 2 only d. 1 and 2 6. All of the properties listed below are characteristic of transition element compounds EXCEPT a. many of them are paramagnetic. b. many of them are colored. c. most of the metals exhibit multiple oxidation states. d. most of the metals upon ionizing lose the d electrons first. e. most of the elements form many complexes. 1

2 7. All of the following molecules or ions are ligands EXCEPT a. H 2 O b. NH + 4 c. Cl - d. CO e. CN - 8. The following complex ions are what kind of isomers? (M = metal; A,B,C and D = ligands) a. ionization d. optical b. geometric e. linkage c. coordination 9. What is the oxidation state of the chromium in [Cr(NH 3 ) 2 (H 2 O) 4 ]Cl 3? a. 0 d. +6 b. +2 e. +9 c What is the geometry of a metal complex with a coordination number of 4? 1. square planar 2. tetrahedral 3. octahedral a. 1 only d. 1 and 2 b. 2 only e. 1, 2, and 3 c. 3 only 11. In octahedral complexes, electrons in 2 of the 5 orbitals ( d 2 z and d 2 2 x - y orbitals) experience a greater repulsion from the lone pairs of electrons on ligands because the d z 2 and d x 2 - y 2 orbitals a. contain more electrons than the other three d-orbitals. b. are oriented directly toward the incoming ligand electron pairs. c. contain only unpaired electrons. d. are the same shape as the orbitals on the ligands. e. are roughly spherical in shape, much as an s-orbital. 12. All of the following statements concerning crystal field theory are true EXCEPT a. in low-spin octahedral complexes, electrons are concentrated in the lower energy d xy, d yz, and d xz orbitals. b. high-spin complexes contain the maximum number of unpaired orbitals. c. ligand-metal bonding is ionic. d. in low-spin complexes, the crystal field splitting energy is large. e. the energy difference between d-orbitals often corresponds to the energy of visible light. 2

3 13. Determine the number of unpaired electrons in an octahedral, low-spin iron(ii) complex. a. 0 b. 1 c. 2 d. 3 e For the compound [Cr(ox) 2 (H 2 O) 2 ]Cl 2, where ox represents the oxalate anion, the coordination number is and the number of ligands is. a. 4,4 c. 4,6 b. 6,4 d. 6,6 15. The spectrochemical series a. relates the oxidation state of a metal to its color. b. lists ligands in order of their tendency to split d-orbitals. c. lists coordination compounds in order of their color. d. lists complex ions in order of their color. e. lists ligands in the order of their color. 16. Which of the following complexes will absorb visible radiation of the shortest wavelength? a. [Co(H 2 O) 6 ] 3+ b. [Co(I) 6 ] 3- c. [Co(OH) 6 ] 3- d. [Co(en) 3 ] 3+ e. [Co(NH 3 ) 6 ] The molar solubility of BaSO 4 is mol/l. What is the value of K sp for BaSO 4? a b c d e The concentration of Ca 2+ in a solution is M. What concentration of CO 2-3 is required to just begin precipitating CaCO 3? The K sp for CaCO 3 is a M b M c M d M e M 3

4 19. A 25.0 ml sample of sulfuric acid is titrated with M NaOH. If the titration requires 35.8 ml of NaOH to reach complete neutralization, what is the molarity of the sulfuric acid solution? a M b M c M d M e M 20. The K sp for BaF 2 is What is the concentration of F - in a saturated solution of BaF 2? a M b M c M d M e M 21. How many grams of solid KF should be added to 1.00 L of M HF to make a buffer of ph = 3.143? (K a for HF = ) a g b g c g d g e g 22. Which of the following pairs of coordination compounds or complex ions are examples of linkage isomers? a. [Cu(NH 3 ) 5 Br]Cl and [Cu(NH 3 ) 5 Cl]Br b. [Fe(NH 3 ) 2 (H 2 O) 4 ]Br 2 and [Fe(NH 3 ) 4 (H 2 O) 2 ]Br 2 c. [Mn(CO) 5 NO 2 ] 2+ and [Mn(CO) 5 ONO] 2+ d. [Fe(NH 3 ) 2 (H 2 O) 4 ]Cl 2 and [Fe(NH 3 ) 2 (H 2 O) 4 ]I 2 e. [Ti(H 2 O) 6 ] 3+ and [Ti(NH 3 ) 6 ] 3+ 4

5 23. Which of the following compounds can exhibit fac-mer isomerism? a. [Cu(CO) 5 I] + b. [Fe(H 2 O) 3 (CO) 3 ] 3+ c. [Ni(CO) 5 NO 2 ] 2+ d. [V(NH 3 ) 2 (H 2 O) 4 ] 2+ e. [Cr(H 2 O) 4 Br 2 ] How many grams of MgF 2 will dissolve in 150. ml of M NaF solution? K sp for MgF 2 = a g b g c g d g e g 25. What is the ph of the solution that results from the addition of 13.0mL of M NaOH to 25.0mL of M HCl during a titration? a b c d e True/False If the following mixtures would result in a good buffer mark (T)rue, if not, mark (F)alse on the exam. (1.5 pts ea) ml 1.0 M KOH with 50. ml 1.0M H 3 PO ml 1.0M NaC 2 H 3 O 2 with 25. ml of HC 2 H 3 O ml 0.50M NaF with 25 ml 0.025M HF ml 1.0M NaCl with 25mL 1.0 M HCl 5

6 Short Answer 30. A buffer is prepared by adding 250 ml of M NaOH to 250 ml of M weak acid, HA. If the ph of the buffer is 8.15, what is the pk a of the acid? (4pts) mL of a buffer solution contains 0.200mmol HX and 0.400mmol NaX. What is the ph change after the addition of 10.0mL of M HCl? (Ka for HX = 7.2 x 10-6 ) (5pts) 6

7 32. What is the concentration of the Cd 2+ (aq) ion in a solution that is M in Cd(NO 3 ) 2 and that is also 1.00M in NH 3 at the instant of mixing? K f for [Cd(NH 3 ) 4 ] 2+ = 1.0 x (5 pts) 33. A volume of 25.0 ml of M HNO 2 is titrated with M NaOH. What is the ph after the addition of 10.5 ml of NaOH? (K a for HNO 2 = ) (5pts) 7

8 34. EXTRA CREDIT: What is the ph of the solution which results from mixing 25 ml of 0.20 M HC 2 H 3 O 2 and 25 ml of 0.20 M NaOH? (K a for HC 2 H 3 O 2 = ) (5 pts) 8

Chem 401 Unit 3 Exam F18 (Buffers, Titrations, Ksp, Transition Metals & Electrochemistry)

Seat #: Date: Chem 401 Unit 3 Exam F18 (Buffers, Titrations, Ksp, Transition Metals & Electrochemistry) Multiple Choice Identify the choice that best completes the statement or answers the question. (4.2pts